Self-tightening fastener



sept. 12, 1944.

E. M. GREEN SELF- T IGHTENING FASTENER Filed Dec. 24, 1942 INVENTOR.1x1/mw Patented sept. 12, i944 vUNITED*A STATES PATENT OFFICESELF-Traumi; FAs'rENEa Emmet M. Green, Los Angeles, Calif. 'ApplicationDecember 24. l1942, semi N0. 469,930

(ci. 24-zzn 7 Claims.

This invention has to do generally with fasteners of the type comprisinga stem or screw adapted to be inserted through and to connect sectionalwork,. one side of which., may be inaccessible, and having at that sideof the work a retaining element releasably holding the stern againstwithdrawal or loosening from the work. More. particularly, 'theinvention is concerned with the stated type of fastener in which athreaded stem is turned into a nut element, and with improved means forpositively assuring against accidental loosening of the fastener fromtightened condition, under all loads and vibrations.

Heretofore it has been proposed to releasably fasten an assembly of worksections by turning into a nut fixed at the inaccessible side of thework, a threaded stem inserted through the work, and to preventaccidental loosening of the stem by resisting longitudinal or axialmovement of the stem out of the nut. Such expedients resist turning ofthe stem out of the nut only indirectly, and to an uncertain degreecontrolled by axial restraint on the stem. It is believed that positiveassurance against accidental loosening of the stem can best be had onlyby direct resistance to the stem rotation, andv by application of aforce constantly seeking to turn the stem in a tightening direction.

Accordingly, one of my primary objects is to provide yielding orspring-acting means applying to the stem when in tightened condition, aforce not only resisting loosening rotation of the stem, but alsoconstantly tending to turn the stem in a tightening direction as anylooseness may develop from vibration, wearing of the parts, or for othercauses. The purposes of the invention may be served in a simple, thoughe typical, manner by forming the inner'end of l the stem, or a portionthereof beyond the nut. with certain shape characteristics forengagement with one or a pair of spring elements, whereby the springsexert against the stem a torque tending to turn the stem into the nut.As

illustrative, the inner end of the stem may have the form of a fiatsided, relatively thin tongue coaxial with the body of the stem andhaving a width suiilcient for the desired turning moment by the springforces applied to the corners of the tongue. As will appear, the shapeof the tongue is of further importance by reason of the fact that itpermits advantage to be taken of the spring thrust throughout a stemturning range approaching 90 degrees.

Another particularly important feature is that of predetermining theposition of the nut with relation to the work thickness, to assure thatthe spring-engaged portion of the stem will assume, when the stem isfully tightened. a position such that the spring elements exert atightening, rather than loosening. eiiect. onthe stem. In thehereinafterdescribed form of the invention, turning of the stem into the nut isalternatelyresisted and aided by the spring thrust. The relationshipbetween the nut position and work thickness however is so predeterminedthat at the point at which the stem head is brought into engagement withthe work, the spring-engaged portion of the stem will be turned to apositionvat which the springs will tend to turn the stem further intothe nut.

Reference may be had to the accompanying drawing for a more completeunderstanding of the stated objects and features, as well as the detailsof a typical embodiment of the invention. In the drawing:

Fig. 1 is a 'plan view of the fastener;

Fig. 2 is an enlarged cross section taken on line 2 2 of Fig. 1;

Fig. 3 is a section'on line 3 3 of Fig. 2;

Fig. 4 is a view similar to'Fig. 1 showing the stem end in neutralposition; and

Fig. 5 is a view, partly in section, illustrating avariational featureof the invention.

As previously indicated, the fastener is applicable to various typesan'd forms of work. Merely as illustrative of a typical embodiment oi'the invention, the fastener assembly is shown to be used for releasablyholding together an assembly of metal sheets In and II havinginner-tting indentations I2 and I3 about an opening Il through which thefastener stem is inserted. The fastener comprises a stem I5 having ahead I6 countersunk within the work indentation and containing a slot I1to receive a screw driver for rotation of the stem into and out ofengagement with the nut element, as will presently appear. The stem I5 fvries a suitable thread designed primarily for adequate bearingengagement with the nut element I9 and for the safe assumption of themaximum load to be trans- -mitted axially of the stem. As illustrative,the

stem may carry a double square-type thread Il extended axially of thestem a distance suiilcient for full engagement with the nut element inthe tightened position of the fastener as shown.

It is contemplated that the stem may be turned into a nut element of anysuitable type and form maintained, at least during threading of the steminto it. in fixed position at the side of the work opposite the head I8.Typically, the nut element i! is shown to comprise a cup-shaped memberhaving lugs secured to the inner work section Il as by rivets 2i, andhaving a portion 22 containing an opening 23 to receive the threads Il.

As best illustrated in Fig. 3, where the nut element Il is maderelatively thin to adapt it for economical manufacture as a stamping,portion 22 may be shaped with the illustrated angularity about theopening 23 so that the nut metal will correspond in thicknesssubstantially to the spac.

ing at 24 between the threads and will follow4 the thread angularitieste ailord maximum bearf ing engagement between the threads and the nutmetal. By virtue of its shape characteristics and proper selection ofthe metal of which it may be formed, the nut element may be madesudiciently strong to support. without appreciable deformationfheavyloads transmitted to it axially of the stem. At this point it may beobserved that the entirety of any force or load tending to separate thework sections il and Il is assumed by the nut element i8, independentlyof the springs resisting turning of the stem out of the nut.

The inner end of the stem il is shaped to form a flattened projection ortongue 2l for engagement with one or a pair of spring elements acting toprevent loosening oi the fastener by positively resisting back-outrotation of the stem. The tongue 25 preferably is formed with ilatsurface sides 2l and may be made relatively thin to permit continuedapplication of the spring force throughout substantially 90 degree stemrotation. The width of the tongue 2l is shown to correspond to the sterndiameter at the base of the threads Il. although it will be understoodthat if desired, the width oi' the tongue may be increased. say to themaximum diameter of the stem threads. As will appear. the tongue 2lserves essentially as a stem-carried eccentric means by reason of itsengageabllity by the springs to impart rotating forces to the stem atpoints offset from the axial center of the stem.

As the stem is turned through the nut element il. the tongue 2l entersbetween a. pair o! spring elements 21 normally disposed in spacedrelation a distance corresponding to about the thickness of thetongue26. so that as the tongue is rotated between the spring elementsthe latter are deilected laterally relative to the stem. If desired, thetongue may be made suiiiciently long that it can be inserted between thesprings before the stem is turned to engage its threads with the nut.While the spring elements may be formed and mounted in any desiredfashion, I prefer to employ a loop form of spring so that its engagementby the tongue 25 will bring into play the resiliency and action of theloop as a whole. Accordingly, the spring elements 21 preferably compriseopposed portions or ends of a spring loop, the annulus 28 ot which ismounted on the nut element i9, as by confinement within a recess orcurved portion 20 of the nut, in which the spring loop is held by lugsIl and Il. In their neutral or reiiexed positions, the springs 21 maysubstantially parallel the tongue 2l and be spaced apart a distancecorresponding to about the thickness of the tongue, all as shown in Fig.4. The spring spacing. as well as proper positioning of the springs withrelation to the tongue. may be assured by providing a spacer lug 31 onthe nutelement I9, the lug being engaged "by the end portion of theannulus 2l. Lugs Il may be spaced from portions 21a of the spring loopsumcientiy to permit tree ilexure of the spring loop to the extent ofits maximum deformation.

In applying the fastener assembly. the stem il is inserted through thework opening Il and the threads il turned through the nut opening 2iuntil the head II is fully seated against the work as shown in thedrawing. During advancement of the stem. the tongue 2l enters betweenthe springs 21 and. depending upon such considerations as the length ofthe tongue, may cause alternate deilcctions oi the springs resisting andthen aiding turning of the stem until the latter is fully inserted. Itmaybe assumed that after entering between the springs. the tongue nrstwill have 100 degrees rotation, during the i'irst 90 degrees of whichthe tongue spreads the springs,

while during the successive I0 degrees the springs converge against thetongue. Upon continued rotation of the tongue through the next 00degrees, the springs are spread and a maximum v distance of spread isreached when, in Fig. i;

the tongue paralleh the'section line 2-1. The position of the nutelement Il is predetermined with reference to the work thickness, or thepoint in the stem advancement at which the head il engages the work. sothat the head seats against the work within the next degrees turning ofthe stem. Thus rigs. i and 2 show the tongue 2l to be turned in theneighborhood of 4.5 degrees beyond the dead center" position. when thehead i6 is fully engaged against the work. In this position of thetongue, springs 21 bear against it at diagonally opposed 'corners andthereby exert a direct rotative force resisting reverse rotation tendingto withdraw or loosen the stem from the nut. Moreover, by reason ofcapacity given the stem or tongue for continued turning in a tighteningdirection under the sustained torque exerted by the springs, vibrationsotherwise tending to create looseness result in progressively tighterengagement of the threads with the nut.

From the foregoing it will be understood how the position of the tonguerelative to the springs when the head II becomes fully seated, ispredetermined in accordance with the spacing of the nut element and thework surface engaged by the screw head. Thus in any given instance, thenut position, axially of the stem. may be predetermined in accordancewith the work thickness. In a similar manner a nut and stem of givendimensons may be adapted for fastening work cf diii'erent thicknesses.by adjusting in accordance with the work thickness. the position oi' thenut element. To illustrate. in applying the nut and stem assembly ofFigs. 1 to 3 to thinner sections of work. see Fig. 5, spacers 3l may beplaced between the nut I0 and the work to maintain the former in properposition to assure turning the tongue 25 to the desired position ofangularlty between the springs 21 when the head I6 is seated against thework.

I claim:

i. A fastener comprising a screw threaded stem adapted to be insertedfrom. one side of the work through an ,opening therein, a fixed nut atthe opposite side oi' the work and receiving the stem thread when thestem is in an initially tightened position so that the stem then mayadvance axia'lly upon rotation to a farther tightened position,eccentric means carried by the stem, and a stem-tightening springsupported independently of the stem at said opposite side of the workand having a portion in engagement with said eccentric means.

assaoos 2. A fastener comprising a screw threaded stem adapted to beinserted from one side of the work through an opening therein, a fixednut at the opposite side of the work and receiving the stem thread whenthe fastener is in tightened condition, eccentric means on the endportion of the stem inserted through the nut, and a stemtighteningspring supported independently of the stem at said opposite side of thework and having a portion in engagement with said eccentric means.

3. A fastener comprising a screw threaded stem adapted to be insertedfrom one side of the work through an opening therein, a xed nut at theopposite side of the work and receiving the stem thread when the stem isin an initially tightened position so that the stem -then may advanceaxially upon rotation to a further tightened position, eccentric meanson the end portion of the stem beyond its threads, and a pair of springssupported independently of the stem at said opposite side of the workand engaging said eccentric means to exert a rotative and tighteningthrust againstthe stem.

4. A fastener comprising a screw threaded stem adapted to be insertedfrom the outside of the work through an opening therein. a head on saidstem engageable against the outside of the work, a xed nut at the insideof the work and receiving the stem thread when the stem is in aninitially tightened. position so that the stem then may advance axiallyupon rotation to a further tightened position, eccentric means carriedby the stem, and a spring supported at said inside of the work andhaving a portion in engagement with said eccentric means to exert arotative and tightening thrust against the stem when said head isengaged against the work.

5. A fastener comprising a stem adapted to be inserted from one side ofthe work through an opening therein, said stem having a screw thread andbeyond said thread a attened tongue, a xed nut at the opposite side ofthe work and receiving the stem thread when the fastener is in tightenedcondition, and a spring supported independently of the stem at saidopposite side of the work and exerting against said iiattened tongue arotative force acting to advance the stem in the nut.

6. A fastener comprising a stem adapted to be inserted through anopening in the work and having a head engageable with one side of thework, said stem having a screw thread and beyond said thread away fromthe head a tongue flattened on opposite sides, a iixed nut at the sideof the work opposite the head engaged side thereof and receiving thestem thread when the fastener is in tightened condition, and springscarried by said nut and engageable with said ilattened sides of thetongue, said springs exerting against the tongue a rotative force actingto advance the stem in the nut.

7. A fastener for sectional work, comprising a stem having a headengageable with one side of the work and carrying a screw thread adaptedto be inserted through an opening in the work, a fixed nut element atthe side of the work opposite said head and into which the stem threadis turned, a flattened tongue forming the end of the stem beyond itsthread and projecting beyond the nut,oppositely disposed springssupported independently of the stem. at said opposite side of the workand engaged by said tongue to resist and then aid turning of the stem.as the stem is turned through successive angles of rotation into the'nutelement, the work thickness and said nut element being so related thatsaid springs are caused to resist rotation of the stem out of the nutelement when said head is brought into engagement with the work.

` EMMET M. GREEN.

